How do I add spoiler tags, change font colours, change font size, highlight, add underlines, ect???
Underlines and such can be done the typical html way.
<u>This Is Underlined</u>
This Is Underlined
The font attributes seem to be stripped and as such can not be done through html tags. For font sizes and such, instead of using proper html, simply use the markdown codes.
# This is an h1
#1 This is an h1
## This is an h2
This is an h2
###### This is an H6
This is an H6
_This is italicized_
This is italicized
For a more comprehensive introduction to markdown, feel free to Google. There are tons of resources out there for it.
As far as spoilers, the staff here would need to add the discourse-spoiler plugin: https://github.com/discourse/discourse-spoiler-alert